Thursday, March 10, 2011

Post Carbon Industrial Process Heat and the SmAHTR

Current energy plans, and energy discussions largely ignore several future energy problems. For example, may industrial processes require significant hear. About 2/3 of the energy used in industry is used in the form of heat. The other third is in the form of electricity, or which a significant portion is transformed into heat. Thus any plan for future energy must acknowledge the need to supply industries with not only electricity but also heat.

For example, the Portland cement manufacture process requires 1450 C heat. Portland Cement is currently manufactured by burning fossil fuels to heat a Kiln in which raw materials are rotated. Given the function of cement in industrial and post-industrial society it is unlikely that cement manufacture will ceases simply if fossil fuel use is drastically curtailed during the 21st century.

Significant amounts of heat are also used in metal manufacturing processes, for example steel, in which a significant amount of coke is used. Iron oxide ores are heated to 1250 C in order to reduce it to Iron, but Iron has to he heated by another 300 C in order to melt it for steel making. However, Steel is now heavily recycled, with scrap steel being melted in Electrical Arc Furnaces. The kicker for the Electrical Arc Furnaces is that they require reliable electrical sources, which make renewable dominated electrical systems unsatisfactory support for processing scrap steel.

The use of solar energy for industrial process heat has been proposed, but there are significant limitations. For example, clouds would greatly limit the usefulness of solare process heat, and thus it would be of very limited use in most of the United States outside the desert Southwest. Even Solar advocates acknowledge that above 250 C solar process heat becomes problematic.

In addition the desert environment which would be hospitable to solar industrial process heat, would be inhospitable to many of the industrial processes in which the solar derived heat might be used. These would include any industrial process which requires large amounts of water. This would man that any industrial process which requires the heating or boiling of large amounts of water would probably be inappropriate for solar heating in desert areas. Although there are many areas in the United States which solar water heating is economically viable for household use, whether solar heating is reliable enough for industrial process use is open to question. It should be noted that on cloudy days and during late afternoon, night and early morning hours, water heating by solar sources must be supplemented by electrical or natural gas water heating. Even in desert environment, solar water heating may require considerable supplementation from other energy sources during fall and winter.

Conventional Nuclear power plants can provide the heat needed for the lower range of industrial requirements, and would not be limited to operations in desert environments, but they would be relatively expensive heat sources. However, nuclear power plants do have large outputs of heated water, that could potentially useful for some industrial uses. Small Modular Reactors, might be appropriate sources of water for industrial process, For Example, the Babcock & Wilcox mPower reactor can be cooled either with an air or a water cooling system. The water cooled mPower offers an extra 11 MWe of electrical capacity per unit, and thus heated water heated water from the mPower may be viewed as economically attractive for industries looking for combined heat and power options for their hot water source.

While Generation III reactors do not produce enough heat to meet many industrial heating requirements, Generation IV reactors are capable of operating at much higher temperatures, thus providing significantly enhanced industrial heating resources. One Generation IV project has reached commercial prototype stage, the Chinese HTR-PM, a 200 MWe pebble bed reactor (video here). At one time, I thought the Pebble Bed Modular Reactor (PBMR) was a promising concept, which offered temperatures of up to 1000 C, with superior safety, and potentially lower cost, but unfortunately there turned out to be some flies in the ointment. The Chinese HTR-PM does appear to offer greatly enhanced heat, but in other respects the design is expensive to build, because PBMR cores are very large, at least twice as large as Light Water Reactor (LWR) cores. This means that PBMRs have massive pressure vessels, relative to their power output. The area of the core enclosed by the PBMR pressure vessel is twice the size of a LWR core. This means that the PBMR core must be built on site, and PBMRs are likely to turn out to be as expensive as LWRs. Still they can produce heat in a range that is attractive for many electrical processes, but at a relatively expensive cost. The problems posed by the PBMR are also present in all helium cooled, graphite moderated Generation IV reactors.

A liquid sodium cooled NPPs represent a second advanced power technology which has some potential for use as an industrial process heat source. It is not clear that a Liquid Sodium cooled reactor would be less expensive than a PBMR while its top heat potential is limited compared to the PBMR. In addition there are both political and technical issues that could inhibit liquid sodium reactor development. Political objections can be raised against liquid sodium reactors on the grounds that they are unsafe and pose proliferation dangers. Neither objection appears to be technically valid, but there is organized and well financed political opposition to liquid sodium reactors, that will probably do everything it can to inhibit their commercial development.

However, there is serious technological problem that could inhibit the large scale deployment. Liquid sodium reactors are fast reactors that require large amounts of fissionable materials in order to reach and maintain criticality. Lets call this the start charge problem. LSFRs offer some potential compensation by breeding nuclear fuel, but this gets us into political problems. The start charge problem means that the initial fuel cost for sodium cooled reactors will be much higher than the initial fuel costs for a thermal reactor. In addition, because so much fissionable materials are required to start LSFRs, only a relatively small number of them can be started without breeding. Thus the LSFR faces high fuel costs, with limited fuel supplies, and/or potential political opposition.

SmAHTR is a 125 MWt, integral primary system FHR concept . . . The design goals for SmAHTR are to deliver safe, affordable, and reliable high-temperature process heat and electricity from a small plant that can be easily transported to and assembled at remote sites. The initial SmAHTR concept is designed to operate with a core outlet temperature of 700°C, but with a system architecture and overall design approach that can be adapted to much higher temperatures as higher-temperature structural materials become available. The SmAHTR reactor vessel is transportable via standard tractor-trailer vehicles to its deployment location . . . .

Diring the SmAHTR design exercise,

Several fuel and core design options for SmAHTR were investigated during the design evolution. . . . A pebble-bed variant is also possible.

One unique feature of the SmAHTR is

an innovative liquid-salt thermal energy storage system, or “salt vault,” . . . expands the flexibility and applicability of the SmAHTR reactor for all applications. The salt vault offers three distinct functionalities: (1) the potential to combine multiple SmAHTR reactor modules to meet thermal energy and electrical power generation demands much greater than 125 MWt, (2) a robust capability to buffer the reactors and the process heat load from transients (such as reactor shutdown or time-varying heat demand) on either side of the salt vault interface, and (3) the ability to buffer multi-reactor module installations from upsets within a single reactor.

One use of the "salt vault" is as a reserve power, peak demand feature. Heated salt can be stored, and then quickly recovered when reserve power is demanded. One useful function of the "salt vault" would be to provide daytime peak demand power, for the relatively brief periods when peak electricity is demanded. Currently peak demand power is provided by natural gas burning turbines, many of which operate with a capacity factor of only 15%. The SmAHTR combined with a "salt vault, opens the door to low cost nuclear peak power generation. Thus a 125 MW SmAHTR is capable of storing 1440 MWe worth of energy over a 24 hour period. With generators operating at a 15% capacity factor, that would mean a 400 MWe output for 3.6 hours a day.

A SmAHTR could be used as

a combined cogeneration mode in which both electricity and process heat are produced.

What can the SmAHTR do? according to the ORNL design team,

The SmAHTR concept described in this report is being designed to be a system capable of providing reliable, economically attractive electricity and process heat. The potential value of such a system improves significantly as the reactor outlet temperature rises above 600°C but requires that fundamental material challenges above this temperature be addressed. In terms of electricity production, thermal-to-electric power conversion efficiencies increase from the mid-thirty percent range at light-water-reactor operating temperatures (~300°C) to the mid-fifty percent range as reactor operating temperatures rise to 750°C—with still higher efficiencies as operating temperatures rise above this level.

With regard to process heat applications, numerous petrochemical refining processes require high-quality heat in the 600–700°C range.1 Small reactor systems operating in the 750°C range would be well suited for remote production of high-pressure steam to enable petroleum extraction from oil sands.2 Hydrogen production via high-temperature electrolysis and steam–methane reforming becomes practical at temperatures in the 800–850°C range (and is currently produced via natural gas combustion).2 The attainment of reactor core outlet temperatures of 900–1000°C would enable a variety of thermal chemical processes for the production of hydrogen from water, gasification of hard coal and lignite, etc.3 Thus, the development of a reliable, economical, and flexible reactor system capable of delivering heat at 600–1000°C would revolutionize highly efficient electrical power production and the production of liquid fuels for transportation and other applications.

It should be noted that there are options for producing heat well above the 1000°C range. These would be include drawing heat in the 600°C to 1000°C range from the reactor and then supplementing it with electrical heating or by hydrogen production and burning.

The ORNL report suggests,

the SmAHTR design goals also include the delivery of acceptable levels of safety, affordability and economic viability from both the plant capital cost and electricity/process heat cost perspectives, and favorable nonproliferation characteristics.

Because the SmAHTR concept involves the use of relatively mature technologies, that have already been prototype tested, its development could be relatively quick, and low cost. Commercialization by 2020 seems possible, with an adequate investment, provided the developer is willing to forgo a Business as usual approach.

4 comments:

Charles - thank you very much for this post. I'm going to be reading the ORNL report with great interest. The 'salt vault' in conjunction with rapid-response turbo generators for supplying peaking power also sounds great. Now if only we'd get to the factory built, modular reactor stage we could get on with building our energy systems properly.

Have there been any studies of energy grid design for optimization of the number, size and siting of energy sources and the required interconnections that delineates the trade-offs in cost and environmental impact? The system goals would have to be elaborated as well. Does anyone out there know of any such work?

Andrew, In addition to ORNL, the idea of a salt vault was developed independently on the Energy from Thorium discussion pages. I picked it up. It is hard to say at present, how much energy would have to be stored in salt vaults. But as far as electrical generation is concerned we would probably have to cover electricity natural gas generators used to provide summer peak demand power. Fleshing out a viable scheme would require a team of researchers, to work out a detailed plan. This is well beyond my capacity. My approach is to develop and idea and hopefully find someone who can carry out the research and planning.